DNA integrity and methylation changes of mouse spermatozoa following prolonged incubation.

Sperm quality can be affected by different factors including the length of incubation time between sperm preparation and intracytoplasmic sperm injection. Here, we have evaluated the level of DNA methylation and expressions of related genes in mice spermatozoa. The spermatozoa were divided into three groups: fresh, spermatozoa incubated at room temperature (RT) and 37°C for 24 hr. The sperm chromatin structure assay was used to determine the DNA fragmentation index (DFI), and DNA methylation was analysed by flow cytometry. The expression levels of DNA methylation-related genes were determined by quantitative real-time PCR (qRT-PCR). According to the results, we observed significantly higher sperm progressive motility and viability in the group incubated at RT compared to the spermatozoa incubated at 37°C (p < 0.05). Spermatozoa incubated at 37°C had a higher DFI compared to the other groups (p < 0.05), but the DNA methylation level significantly decreased (p < 0.05). qRT-PCR analysis showed increased Dnmt-1 expression in spermatozoa after 24-hr incubation at 37°C. However, there were significantly higher expression levels of Dnmt-3l, Dnmt-3a and Dnmt-3b after incubation at both RT and 37°C compared to the fresh group (p < 0.05). The 24-hr incubation period affected both sperm DNA methylation and integrity. This study indicated that incubation at RT resulted in better sperm quality.